Temporally modulated lighting system and method

ABSTRACT

Electric light sources typically exhibit temporal variations in luminous flux output, commonly referred to as “flicker.” Flicker, or temporal modulation, is known to influence the growth, health and behavior patterns of humans, and is also linked to growth, health and behavior patterns throughout the growth cycle of plants and animals. Control of peak radiant flux emitted by a light source to temporally modulate a light source will allow for the control of plants and animals for sustainable farming including but not limited to horticultural, agricultural, or aquacultural endeavors. The light source allows the transmission of daylight, which is combined with the flicker.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of application Ser. No.15/491,166 filed on 19 Apr. 2017 and claims benefit of U.S. provisionalSer. No. 62/324,404 filed 19 Apr. 2016, both of which are incorporatedby reference herein in their entireties.

TECHNICAL FIELD

The subject matter of the present invention relates to the field ofbiological lighting systems and more particularly, is concerned with thebeneficial aspects of electric light source flicker for plants andanimals for sustainable farming, including but not limited tohorticultural, agricultural, and aquacultural endeavors.

BACKGROUND

Electric light sources powered by alternating current power sourcestypically exhibit temporal variations in luminous flux output, commonlyreferred to as “flicker.” Depending on the alternating currentfrequency, the ratio of maximum to minimum luminous flux output, and themodulation waveform, flicker may be perceived as being a moderately toseverely annoying visual artifacts that needs to be alleviated oreliminated.

Vision research to date, however, has mostly focused on the humanaspects of visual flicker. Light sources with rapid temporal variationsdo not occur in nature, and so both animals and plants may exhibitphysiological and psychological responses to flickering electric lightsources that may be detrimental or beneficial.

Animal husbandry and horticulture in particular are two fields wheresuch physiological and psychological responses may impact the health andwellbeing of the animals and plants, and thereby engender economicbenefits and risks. The present invention therefore seeks to addressthese issues with a system and method for controlling flicker.

SUMMARY

Disclosed herein is a method for temporally modulating a light sourcefor plants wherein the peak radiant flux emitted by a light source canbe temporally modulated according to a plant's photopigments andcellular mechanisms to control the response by the plant to electriclight source flicker.

Also disclosed herein is a system for temporally modulating a lightsource for plants wherein: at least one response variable is monitoredand the resultant signal incorporated in a closed loop feedback system;and the parameters of the temporally modulated lighting system adjusted.

Further disclosed is a system for optimizing health of a plantcomprising: a glazing unit having: an outer pane; an inner pane parallelto and spaced apart from the outer pane; an array of light-emittingelements (LEEs) mounted on an inner side of the outer pane; andtransparent electrical conductors adhered to the inner side of the outerpane and connected to the LEEs; a sensor that detects a health parameterof the plant; and a controller connected via the transparent electricalconductors to the LEEs, wherein the controller: controls the LEEs toprovide flicker that has a peak radiant flux, an average radiant flux, aduty factor and a pulse frequency, wherein the plant is exposed to theflicker; incorporates a signal from the sensor into a closed loopfeedback system; and adjusts, based on the detected health parameter:the peak radiant flux and the duty factor, without adjusting the pulsefrequency and the average radiant flux; or the pulse frequency, withoutadjusting the peak radiant flux, the duty factor and the average radiantflux; wherein said adjustment maintains the health parameter of theplant within predetermined limits.

A method for optimizing health of a plant comprising: providing theplant; exposing the plant to flicker from a glazing unit having: anouter pane; an inner pane parallel to and spaced apart from the outerpane; an array of light-emitting elements (LEEs) mounted on an innerside of the outer pane; and transparent electrical conductors adhered tothe inner side of the outer pane and connected to the LEEs; wherein theflicker has a peak radiant flux, an average radiant flux, a duty factorand a pulse frequency, wherein the plant is exposed to the flicker;detecting a health parameter of the plant; and adjusting, based on thedetected health parameter: the peak radiant flux and the duty factor,without adjusting the pulse frequency and the average radiant flux; orthe pulse frequency, without adjusting the peak radiant flux, the dutyfactor and the average radiant flux; wherein said adjustment maintainsthe health parameter of the plant within predetermined limits.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the prior art measured temporal contrast sensitivityfunction of the human visual system.

FIG. 2 shows four example pulse width modulation waveforms that exhibitdifferent duty cycles but result in constant average radiant flux.

FIG. 3 shows a flowchart for a closed loop feedback system capable ofmaintaining optimal plant growth.

FIG. 4 shows a trainable neural network controller that learns optimalsettings for temporally modulated light sources.

FIG. 5 shows a section of double-paned glazing with light-emittingelements and an optical diffuser.

FIG. 6 shows a section of double-paned glazing with light-emittingelements and a holographic diffuser.

DETAILED DESCRIPTION

The present invention is herein described more fully with reference tothe accompanying drawings, in which embodiments of the invention areshown. This invention may, however, be embodied in many different forms,and should not be construed as limited to the embodiments describedherein. Rather, these embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope of theinvention to those skilled in the art.

For the purposes of this application, sustainable farming is theproduction of food, fiber, or other plant or animal products usingtechniques that aim to protect the environment, public health, humancommunities, and animal welfare. Sustainable farming includes but is notlimited to horticultural, agricultural, and aquacultural endeavors,including animal husbandry. Any reference to sustainable farmingincludes one or more, or collectively all, of these endeavors.

The perception of electric light flicker by the human visual system hasbeen studied for more than a century (e.g., Greene 2013). It is widelyknown that human sensitivity to flicker increases with increasingfrequency from one or two Hertz up to approximately 20 to 30 Hertz,depending on the level retinal illuminance, then decreases rapidly forhigher frequencies. It is also known that in humans peripheral vision ismore sensitive than central vision to flicker.

The “critical fusion frequency” (CFF) is defined as the frequency atwhich a flashing light source is perceived as a steady rather than anintermittent visual stimulus. This frequency varies with stimulus size,shape, retinal location, adaptation luminance, and modulation depth, butrarely exceeds 60 Hertz, even with a large visual area with 100 percentmodulation, seen with a high adaptation luminance.

Flicker above the CFF can be indirectly perceived as blur in the case ofhigh-speed motion, either with perceived objects or rapid eye movement.Stroboscopes in particular take advantage of this psychophysiologicalphenomenon to render quickly rotating objects as appearing to be staticor slowly rotating. Bullough et al. (2013) have shown that thestroboscopic effects of light source flicker are detectable forfrequencies as high as one kilohertz.

Even when not visually noticeable, flicker has been implicated inadverse health effects, including headaches, fatigue, blurred vision,eyestrain, migraines, reduced visual task performance, as well asincreases in autistic behaviors in children and neurological problems,including epileptic seizures.

With the introduction of semiconductor light-emitting diodes for generallighting applications, the effects of visual flicker on both perceptionand health and wellbeing has recently become of increased concern tolighting designers (e.g., IEEE 2015. Perrin et al. 2016).

Compared to human perception of visual flicker, less research has beenconducted on the perception of flicker by animals (e.g., Bostrom et al.2016, Healy et al. 2013, Inger et al. 2014, Lisney et al. 2012).

The animal research has focused on measuring the CFF of various species(e.g., Inger et al. 2014), but there does not appear to be any researchon the long-term psychological and physiological impacts of flicker ondomestic animals kept under constant electric lighting, even though itis acknowledged as a possibility by, for example, Lisney et al. (2012)in relation to fluorescent lighting.

As for plants, Lefsrud and Kopsall (2006) consider only time periods ofhours to minutes for on-off cycles of horticultural lighting.

For animals, sensitivity to light is mediated by light-sensitiveproteins called “opsins.” More than one thousand opsins have beenidentified to date, and occur in not only animals, but also archaea,bacteria, fungi, and certain algae (Terakita 2005). In humans, at leastfive opsins—rhodopsin, long-, medium-, and short-wave opsins,melanopsin, and neuropsin—are responsible for both visual and non-visuallight and ultraviolet radiation sensitivity. A complex series ofphotochemical reactions and neural responses mediate ourpsychophysiological responses to varying light conditions, with responsetimes ranging from picoseconds to minutes. While there are manydifferent opsins present in the light-sensitive organs of other animalspecies, they all perform similar functions.

For plants, various photopigments are sensitive to light, includingchlorophyll A and B (responsible for photosynthesis), phytochrome(responsible for plant photomorphogenesis), cryptochromes, and manydifferent carotenoids, including xanthophylls and carotenes, that bothassist in photosynthesis and protect chlorophyll from damage byultraviolet radiation and blue light.

Phytochrome in particular has two isoforms, designated P_(r) and P_(fr),that function as a photosensitive switch when alternately to red (˜625nm) and far red (˜730 nm) electromagnetic radiation. This switchregulates a wide variety of physiological functions in plants, includingseed germination, shoot growth, flowering, leaf expansion andabscission, and bud dormancy. Borthwick et al. (1952) demonstrated thatlight pulses as short as one minute are sufficient to disrupt thesefunctions, thereby influencing plant growth. There are at least 600known carotenoids, and it is not known whether any of them similarlyfunction as photosensitive switches. It is also not known whether thereis an upper limit to the exposure frequency for phytochrome in vivo, andthe effect this may have on plant development. Effects may range fromobvious changes in plant morphology to temporal changes in plantdevelopment and the production of plant biomass, nutrients, aromatics,or desirable pharmaceutical compounds.

Plants have also evolved various strategies for dissipating the excessenergy received from sunlight. Müller et al. (2001), for example,discuss non-photochemical mechanisms whereby chlorophyll moleculesdissipate excess excitation energy as heat.

Plant photopigments and cellular mechanisms will respond in various waysto electric light source flicker, with modulation frequenciespotentially ranging from tens of seconds to megahertz. As one example, aplant species irradiated with electromagnetic radiation with amodulation frequency of one to ten kilohertz and a small pulse widthduty factor may respond differently over its growth cycle compared tothe same species irradiated with constant radiation, even though theirradiance and spectral power distribution may be the same.

Plant biologists and horticulturalists have observed that differentplant species respond differently to the same lighting conditions. Giventhis, determining the responses of the many different plant species totemporally modulated electromagnetic radiation may require additionalexperimentation. Nevertheless, the basic principles of a novel lightingsystem can be disclosed that take advantage of these responses.

In one embodiment, the peak radiant flux emitted by a light source canbe temporally modulated. For example, the peak drive current deliveredto a semiconductor light-emitting diode may be controlled by analogcircuitry. Alternatively, the drive current may be digitally modulatedat a high frequency that does not influence the plant response.

The average radiant flux emitted by a light source can additionally betemporally modulated. For example, the duty cycle of a pulse widthmodulation current delivered to a semiconductor light-emitting diode maybe controlled by digital circuitry. With 100 percent duty cycle, thelight source will deliver constant irradiance for the plant at a levelthat it can tolerate. Conversely, with say 20 percent duty cycle and 5times the peak level, the light source will deliver the same averageirradiance, but with peak irradiance such that the plant is forced todissipate the excess energy received during each pulse.

The waveform of the temporally modulated flux may be an on-off squarewave with a variable duty factor. A more complex waveform may also beemployed.

FIG. 2 shows four examples of pulse width modulation (PWM) waveformsthat exhibit different duty cycles but result in constant averageradiant flux.

In one embodiment, the peak radiant flux can be controlled by an analogconstant current driver while the average radiant flux is controlled byan additional digital constant current driver. As an example, 200 showsa pulse width modulated (PWM) waveform with a 20 percent duty factor,while 210 shows a PWM waveform with 80 percent duty factor and a peakoutput that is 25 percent of that shown in 200. Consequently, bothwaveforms result in the same average radiant flux.

In another embodiment, the peak radiant flux can be controlled by ahigh-frequency digital constant current driver while the average radiantflux is controlled by an additional digital constant current driver witha lower frequency signal that is superimposed on the high frequencysignal. (As an example, 220 shows a pulse width modulated (PWM) waveformwith a 20 percent duty factor, while 230 shows a PWM waveform with fourevenly-spaced pulses, each exhibiting 5 percent duty factors and thesame peak output as that shown in 220. Consequently, both waveformsagain result in the same average radiant flux.)

In a preferred embodiment, only selected regions of the electromagneticradiation spectrum are temporally modulated. Many plant photopigmentshave narrow spectral responsivity bandwidths, and so it is advantageousto provide temporally modulated irradiance within these spectral bandswhile otherwise providing constant irradiance across the biologicallyactive spectrum. Similarly, it is advantageous to modulate differentbands with different frequencies, and with different peak and averageradiant flux.

Changes in modulation over the growth cycle of a plant species may alsobe implemented to take into account the changes in plants physiologyduring the plant growth cycle, including plant photopigments. Thisresults in a need to modify the regions of the electromagnetic radiationspectrum as a plant matures. Plant maturity may include the stages fromgermination to seedling, to young plant, to mature plant. Similarchanges in modulation as animals or fish mature may also be implementedto take into account the changes in animal physiology and behaviorduring growth.

In another embodiment the temporal modulation frequency or frequencies,peak and average radiant fluxes, and spectral power distribution arevaried on a diurnal day-night basis (which is not necessarily 24 hoursin length), and over the growth cycle of the species being grown underthe lighting conditions.

In another embodiment the temporally modulated electric lighting iscombined with constant electric lighting.

The temporally modulated electric lighting may be combined with naturaldaylight.

The temporally modulated electric lighting may be combined with naturaldaylight and supplemental electric lighting.

The temporally modulated electric lighting may be combined with naturaldaylight or natural daylight and supplemental electric lighting througha daylight harvesting system. A daylight harvesting system may include acombination of hardware and software used to maximize the effectivenessand/or efficiency of electric lighting in conjunction with naturaldaylight.

Temporally modulated lighting may be provided by variable transmittancewindows, such as for example electrochromic windows or a system ofautomated blinds and louvers.

In one embodiment one or more response variables is monitored and theresultant signal incorporated in a closed loop feedback system, whereinthe parameters of the temporally modulated lighting system may beadjusted to optimize system performance. As an example, the chlorophyllfluorescence of a plant may be monitored as an indication of planthealth, and the pulse width modulation frequency or duty cycle adjustedusing a proportional-integral-derivative (PID) control algorithm tomaintain plant health.

As an example, FIG. 3 shows a flowchart for a closed loop feedbacksystem wherein the PWM duty factor is periodically adjusted such thatthe measured chlorophyll fluorescence of a plant is maintained withindesired limits during plant growth.

One or more response variables may be monitored and the resultant signalincorporated in a fuzzy logic or neural network control system withartificial intelligence capabilities that can learn optimum combinationsof system parameter settings for different plant species and predictoptimal settings based on observed temporal trends in systemperformance.

As an example, FIG. 4 shows a trainable neural network controller 400that sets the peak amplitude and duty cycle of light source controller410, which provides temporally modulated drive current to light source420. Light source 420 irradiates plant 430 with biologically activeradiation, causing the plant to grow. Sensor 440 detects a plant growthand health parameter, such as for example chlorophyll fluorescence orfruit color. Sensor controller 450 periodically samples the signal fromsensor 440 and provides the data as input to neural network controller400.

The windows that are used for providing temporally modulated lighting tothe plants may also include sources of light for producing the flicker.Another such embodiment is shown in FIG. 5, wherein an assembly 500,which is a glazing unit, includes a spaced array of temporally-modulatedlight-emitting elements (LEEs) 510 that are mechanically coupled to afirst transparent substrate 520 and electrically connected totransparent conductors 530, and wherein said first transparent substrate520 is proximate and parallel to a second transparent substrate 540. Thefirst transparent substrate 520 may be referred to as the outer pane ofthe assembly 500, and the second transparent substrate 540 may bereferred to as the inner pane. In some embodiments, the conductors 530are not transparent, as they can be made narrow enough not to blocksignificant daylight passing through while still carrying adequatecurrent to sufficiently illuminate the LEEs. In some embodiments, theconductors may be translucent, or substantially transparent so thattheir effect on the daylight passing through the glazing unit isnegligible.

While the embodiments herein reference plants specifically, the sametechniques can be applied to animals for sustainable farming, includingbut not limited to horticultural, agricultural, and aquaculturalendeavors. The use of flicker to stress and destress animals and fishmay also have a beneficial or negative impact in terms of sustainablefarming (example, while human awareness of flicker is around 100 Hz,chickens will see flicker well beyond humans up to around 300 Hz, sothat they are essentially living in a strobe light under HPS (highpressure sodium) lamps. Fish and other animals are be similarly affectedby flicker.

Additionally, the same techniques can be applied as a health benefit forhumans. The control of flicker to reduce stress and improve overallhealth in humans can be monitored and employed in differentenvironments, including for example office buildings, industrialcomplexes, commercial areas, and residential areas.

In an embodiment, said assembly 500 is a double-pane glazing unit,wherein the transparent substrates 520, 540 are fabricated from, forexample, soda-lime glass, borosilicate glass, or polymethyl methacrylate(PMMA), and the space between them is evacuated or filled with athermally insulating gas such as argon. The separation 550 between theLEEs is chosen such that the maximum amount of daylight 560 istransmitted by the assembly 500 while simultaneously maximizing theamount of light 570 that can be emitted by the LEEs commensurate withthe need to dissipate thermally-conductive heat through substrate 520.Daylight, or other ambient light, is incident on the outside of theouter pane of the assembly 500 and passes through the assembly 500 toemerge from the inner pane. The light 570 that is emitted from the LEEs510 also emerges from the assembly 500 from the inner pane, so that thedaylight 560 and light 570 from the LEEs are combined to illuminate theplants.

In another embodiment, the glazing unit may include more than two panes.In addition, fluid may be included between the panes. Such fluid mayinclude gas, such as air or argon for thermal insulation, laminar waterflow or even index-matching oil such as mineral spirits to improvethermal heat transfer. The flow may be achieved, for example, byincluding a pump in the assembly 500. The fluid may also have propertiesthat affect the light, including ambient (external) and supplemental(internal) light, including the transmissive, diffusion, and reflectiveproperties of the fluid. The fluid or fluids may be tuned to increasethe effectiveness of ambient and supplemental lighting.

In an embodiment, transparent substrate 540 is an optical diffusercomprised of, for example, a transparent substrate with an etched (orotherwise textured) surface or a bulk material with embedded diffusingparticles. In other embodiments, the surface of the transparentsubstrate 540 may be textured by embossing a pattern thereon. In someembodiments, the textured surface may be provided on PMMA by theapplication of holographic diffuser patterns.

In a similar embodiment, transparent substrate 540 is an opticaldiffuser comprised of, for example, a transparent substrate with anetched surface or a bulk material with embedded diffusing particles,wherein said particles are luminophores that are excited by photonswithin a first range of wavelengths (the “excitation” spectrum) andre-emit photons within a second range of wavelengths (the “emission”spectrum). Such an embodiment is useful, for example, in greenhouseglazing wherein the luminophores absorb blue light from incidentdaylight or light emitted by quasimonochromatic LEEs (such as bluelight-emitting diodes) and convert it into red light that is morereadily absorbed by plants for photosynthesis. When the luminophores arefluorophores, phosphors or quantum dots with suitably short decay times,the temporal flickering of the LEEs will be preserved.

Another embodiment is shown in FIG. 6, wherein an assembly 600 issimilarly comprised of a spaced array of temporally-modulatedlight-emitting elements (LEEs) 610 that are mechanically coupled to afirst transparent substrate 620 and electrically connected totransparent conductors 630, wherein said first transparent substrate 620is proximate and parallel to a second transparent substrate 640, andwhere a holographic diffuser 650 is optically coupled to transparentsubstrate 640.

An advantage of the holographic diffuser 650 is that, as disclosed byTedesco (U.S. Pat. No. 5,861,990), it both diffuses and concentratesincident light. Thus, for example, a greenhouse that is aligned on anapproximate east-west axis may be provided with holographic diffusers onits roof panels such that more daylight is directed into the greenhousewhen the incident direct sunlight is at large acute angles such as occurin the early morning and late afternoon. Holographic diffusers may beengineered to exhibit circular, elliptical or linear diffusioncharacteristics, as disclosed by, for example, Santoro in U.S. Pat. No.7,660,039. The degree of diffusion (both eccentricity and full-widthhalf-maximum angle) and diffuser orientation (for elliptical and linearholographic diffusers) may therefore be selected based on greenhousealignment, roof style, and historical weather data to determine theexpected availability of direct sunlight per month.

The term “light-emitting element” (or “LEE”) is defined as any devicethat emits electromagnetic radiation at a wavelength or within awavelength regime of interest, for example, a visible, infrared orultraviolet regime, when activated by applying a potential differenceacross the device and/or passing a current through the device. Examplesof LEEs include solid-state, organic, polymer, phosphor-coated orhigh-flux LEDs, laser diodes, and other similar devices as would bereadily understood. The emitted radiation of a LEE may be visible, suchas red, blue, or green, or invisible, such as infrared or ultraviolet. ALEE may produce radiation of a spread of wavelengths. A LEE may includea phosphorescent or fluorescent material for converting a portion of itsemissions from one set of wavelengths to another. A LEE may includemultiple LEEs, each emitting essentially the same or differentwavelengths. A LEE may also feature an optic that redirects lightemitted by the semiconductor die in preferred directions. The optic maybe a refractive or diffractive optical element that is molded orembossed onto the die or its supporting (typically transparent)substrate. A lateral dimension of the optic may be, e.g., less than orapproximately equal to the spacing between LEEs (within an array ofLEEs), for example between approximately 1 mm and approximately 10 mm.

A LEE may be of any size. In some embodiments, a LEE has one lateraldimension less than 500 μm. Exemplary sizes of a LEE may include about250 μm by about 600 μm, about 250 μm by about 400 μm, about 250 μm byabout 300 μm, or about 225 μm by about 175 μm. In some embodiments, aLEE includes or consists essentially of a small LED die, also referredto as a “microLED.” A microLED generally has one lateral dimension lessthan about 300 μm. In some embodiments, the LEE has one lateraldimension less than about 200 μm or even less than about 100 μm. Forexample, a microLED may have a size of about 225 μm by about 175 μm orabout 150 μm by about 100 μm or about 150 μm by about 50 μm. In someembodiments, the surface area of the top surface of a microLED is lessthan 50,000 μm² or less than 10,000 μm².

While LEEs have been used as examples of elements that may be used inembodiments of the present invention, other semiconductor die may alsobe used instead of or in addition to such devices. For example,photovoltaic cells (for example single junction or multijunction cells),transistors, photodiodes, laser diodes, resistors, capacitors,non-emitting diodes, and/or sensors may be utilized. As used herein,“phosphor” refers to any material that shifts the wavelength of lightirradiating it and/or that is luminescent, fluorescent, and/orphosphorescent. Phosphors may be in the form of powders or particles andin such case may be mixed in binders, e.g., silicone. As used herein,phosphor may refer to the powder or particles or to the powder orparticles plus binder.

Any one or more response variables monitored, and any input data, may becollected as data and stored in a database locally, transmitted,including wireless transmission, to an offsite database, or stored ortransmitted in a means that will allow import into a database. Theavailability and accessibility of this data may allow for furtherrefinements within the system, and additional study of the results.

While this disclosure discusses temporally modulated lighting in termsof plant growth in greenhouses and vertical farms, the invention mayalso be applied to animal husbandry applications, included but notlimited to aviaries, poultry farms, aquaculture farms, fresh andsaltwater aquaria, and insects raised for protein (food), pest control,and pharmaceutical purposes.

We claim:
 1. A system for optimizing health of a plant comprising: aglazing unit having: an outer pane; an inner pane parallel to and spacedapart from the outer pane; an array of light-emitting elements (LEEs)mounted on an inner side of the outer pane; and electrical conductorsadhered to the inner side of the outer pane and connected to the LEEs; asensor that detects a health parameter of the plant; a current driverthat provides current to the glazing unit; and a controller connectedvia the current driver and the electrical conductors to the LEEs,wherein the controller: controls the LEEs to provide flicker that has apeak radiant flux, an average radiant flux, a duty factor and a pulsefrequency, wherein the plant is exposed to the flicker; provides amodulated first frequency signal for controlling the peak radiant flux:provides a modulated second frequency signal for controlling the averageradiant flux, wherein the second frequency is lower than the firstfrequency and superimposed on the first frequency and wherein thecurrent is modulated with the superimposed first and second frequencies;incorporates a signal from the sensor into a closed loop feedbacksystem; and adjusts, based on the detected health parameter: the peakradiant flux and the duty factor, without adjusting the pulse frequencyand the average radiant flux; or the pulse frequency, without adjustingthe peak radiant flux, the duty factor and the average radiant flux;wherein said adjustment maintains the health parameter of the plantwithin predetermined limits.
 2. The system of claim 1 wherein the innerpane transmits light that has passed through the outer pane and lightthat is emitted from the LEEs.
 3. The system of claim 1 wherein theouter pane and the inner pane are soda-lime glass or borosilicate glass.4. The system of claim 1 wherein the electrical conductors aresubstantially transparent.
 5. The system of claim 1 wherein the outerpane and the inner pane are polymethyl methacrylate.
 6. The system ofclaim 1 wherein a space between the outer pane and the inner pane isfilled with air or argon.
 7. The system of claim 1 wherein a spacebetween the outer pane and the inner pane is filled with liquid.
 8. Thesystem of claim 7, wherein the liquid is water.
 9. The system of claim7, wherein the liquid is mineral spirits.
 10. The system of claim 7,wherein the liquid is flowing.
 11. The system of claim 1, wherein theinner pane is an optical diffuser.
 12. The system of claim 11, whereinthe optical diffuser comprises a transparent substrate with a texturedsurface.
 13. The system of claim 11, wherein the optical diffusercomprises a material with embedded diffusing particles.
 14. The systemof claim 13, wherein the diffusing particles are luminophores.
 15. Thesystem of claim 14, wherein the luminophores are fluorophores, phosphorsor quantum dots that have a decay time shorter than an off-cycle of theflicker.
 16. The system of claim 1, further comprising a holographicdiffuser on an inner surface of the inner pane.
 17. The system of claim1, wherein the LEEs are micro light emitting diodes.
 18. A method foroptimizing health of a plant comprising: providing the plant; exposingthe plant to flicker from a glazing unit having: an outer pane; an innerpane parallel to and spaced apart from the outer pane; an array oflight-emitting elements (LEEs) mounted on an inner side of the outerpane; and electrical conductors adhered to the inner side of the outerpane and connected to the LEEs; wherein the flicker has a peak radiantflux, an average radiant flux, a duty factor and a pulse frequency;providing, by a first current driver, a modulated first frequency signalfor controlling the peak radiant flux; providing, by a second currentdriver, a modulated second frequency signal for controlling the averageradiant flux, wherein the second frequency is lower than the firstfrequency and superimposed on the first frequency; detecting a healthparameter of the plant; and adjusting, based on the detected healthparameter: the peak radiant flux and the duty factor, without adjustingthe pulse frequency and the average radiant flux; or the pulsefrequency, without adjusting the peak radiant flux, the duty factor andthe average radiant flux; wherein said adjustment maintains the healthparameter of the plant within predetermined limits.